Spring has sprung. It won't be long before we tootle to park and dale, open the heavy hampers and unfurl the itchy rugs, bat away the wasps and begin the sodden blustery tradition of the great British picnic.

And what could be more quintessential to that event than the humble scotch egg? Extraordinary things. In the past, they went from rich man's caprice to Victorian savoury. Now they inhabit a strange hinterland between pubby ubiquity and zhooshed-up gastro cliche.Gary Rhodes airily opines in one of his cookbooks: "It doesn't take much to work out where scotch eggs were born. They are a Scottish speciality." Nonsense, Gary. Fortnum & Mason created the egg in 1738 as a portable snack for coach travellers heading west from London along Piccadilly. I spoke with Fortnum's archivist, Dr Andrea Tanner, who said: "the eggs would have been smaller in those days: pullet's rather than hen's eggs. The meat would also have been gamier, like a strong, coarse liver pâté."

Scotch eggs filtered steadily down the social ranks: they grew more common – in both senses – with cheaper Victorian meat, and were thence exported abroad. Mr Bigg's, a Nigerian fast food chain, today serves them alongside "heritage pottage" and jollof rice. Scotch eggs on sticks are classics of the Minnesota State Fair and, according to this online forum, "skotchi eggu" are a staple of Japanese new year (recipe here).

In a classic scotch egg, a cold, granular carapace clags pulped, ashen roadkill, a firm egg white and a pale pappy yolk. Green-tinged, sulphuric and ghastly, it lends itself well to English comedy. The egg was Keith's trademark in The Office, a joke the writers repeated three times across the series. When a post-egg Alan Partridge breathes gassily into his PA's face, he says sadly: "It's going to be in the system till about four". And even the "comedian" Frankie Boyle understands his trade enough to recognise the humour inherent in the scotch egg. Why?

"Everyone has eaten a bad one," says Stephen Williams, head chef at the Harwood Arms in Fulham, which is justly famous for its soft-boiled venison scotch eggs. "They're staples of school dinners and motorway service stations, so people are very surprised when they taste a nice one."

Food blogger Helen Graves has conducted experiments pitching fried against baked scotch eggs and points out their ubiquity: "They used to be comedy snacks: grey egg, mystery meat interior and suspiciously hued crumb. Now they're default gastropub fodder." Heston Blumenthal serves a quail's egg version at his pub in Bray, while a soft-boiled model is the signature of the Coach and Horses in Clerkenwell. Guy Dimond, Time Out's chief restaurant critic, has written: "The scotch egg revival has become an epidemic across London," and Fay Maschler says wearily: "Every gastropub is knee-deep in them." I agree, but reckon the Harwood's deserves its fame.

The point, of course, is that these eggs can be delicious. They work as a kind of miniaturised fry-up, and as an improvement on nature: inedible shells rendered crisp and crunchy, buttressed by sausagemeat, with a lovely cooked egg. "It's a complete little parcel," says Stephen Williams. "You use your hands to eat them, so they're informal and relax the table. And in our ones, the yolk dribbles down your chin – they're just fun."